Optical tweezers for signal detection and micromanipulation

The work presented in this thesis explores new multi-disciplinary applications of optical tweezers in the physical and biological sciences. Firstly, the three dimensional trapping of partially silvered sphere in a standard TEM00 optical trap was characterised. These spheres were then coated with an azo dye such that surface-enhanced resonance Raman (SERRS) measurements could be made on a single bead whilst it was simultaneously trapped in 532 nm optical tweezers. The length of time over which the SERRS signal could be recorded was increased, from milli-seconds to minutes, by using 1064 nm optical tweezers and introducing second harmonic light, generated via a frequency doubling crystal, for the excitation of the SERRS signal. In addition to trapping single particles, a spatial light modulator (SLM) was introduced into the optical tweezers to produce holographic optical tweezers. The SLM allowed the creation and manipulation of several optical beams both simultaneously and independently of each other. Three dimensional trapping and manipulation of multiple micron-sized spheres were achieved using the SLM in the Fourier plane of the traps. This ability to trap and manipulate objects, such as fluorescent spheres and E. coli, in 3D was extended to create permanent 3D structures that were set within a polymer matrix. These objects could be created, permanently set and imaged ex-situ. A summary of conclusions and ideas for future work are included